A conjugate is formed by changing the sign of the second term in a binomial. $$\begin{array}{cc}\text{Binomial}& \text{Conjugate}\\ x+2& x-2\\ \text{-}n-1& \text{-}n+1\\ f+3g& f-3g\\ a+bi& a-bi\end{array}$$ Two binomials that are conjugates of one another are generally called a conjugate pair. Note that complex conjugates are also formed according to this rule.